The worldwide in-building coverage market (IBW), or Distributed antenna system (DAS), as it is frequently called, has been constantly growing in the past few years. It is quickly becoming the major arena in which mobile operators' revenues are generated. Most of the calls and data transfers are now generated inside buildings and constitute around 80% of the operators' revenues.
In parallel to that, and due to the intensive use of smart phones, tablets, etc., data carrying capacity is quickly becoming a valuable and scarce resource. The demand for capacity has been constantly growing at a huge rate of around 100% per year. This means that a DAS system installed today will require twice the capacity a year from now and will require 8 times more capacity three years from now.
The aforesaid facts are valid not only for indoor DAS but also for outdoor DAS's particularly when serving multiple operators in confined areas such as campuses, stadiums, etc. DAS's which were focused in the past on providing coverage are now focused on providing capacity as well as coverage. One skilled in the art is well aware that the data throughput of the BTSs depends heavily on the signal to noise ratios in the uplink channels. The better the signal to noise ratio, the higher is the data throughput that can be handled by the BTS.
Therefore a critical step in installing and commissioning a DAS is ensuring that there are no uplink interferences and no excessive noise is present in the uplink channels of the DAS not just during the initial commissioning phase. Needless to say that during the life cycle of the DAS, the issue of uplink noise and interferences should be addressed on a regular basis.
There are quite a few sources that may generate uplink interference or excessive uplink noise in a DAS installation. Some of them are listed below:                PIM (Passive Intermodulation products) generated at objects that are close to the DAS transmitting antenna and thus generate reflections back to the uplink channels of the DAS        PIM generated at the DAS antenna        PIM generated at the DAS connectors and cables. There are multiple antenna and cables connections in a DAS. Each connector which is not connected properly may cause PIM issues;        PIM generated in the duplexers of the DAS RRUs;        IMDs (intermodulation distortion) generated in the downlink MCPAs (Multi Carrier Power Amplifiers) of the DAS. RRUs in uplink frequencies, which may leak to the DAS uplink channels for example through the limited isolation of the cavity or ceramic duplexers or any other duplexers.        Noise leakage from Downlink MCPAs to the uplink channels.        Any external interference in the vicinity of the DAS antenna transmitting in the uplink frequencies which may penetrate the DAS uplink channels through the DAS antenna.        
Therefore, as part of the DAS commissioning phase, DAS installers struggle to perform PIM and noise level field measurements in the uplink channels to ascertain that there are no PIM nor excessive noise nor interferences in the uplink channels. This is a very tedious, laborious, and costly task which has to be performed in the field as part of the commissioning process. What makes it especially cumbersome is when a real problem is found. The tasks of analyzing the problem in the field and trying to isolate the source of the problem in a DAS where there may be hundreds or even thousands of antenna and cable connectors is very laborious and very expensive.